A method for simultaneous determination of AV and R and applications

A method for the simultaneous determination of the interstellar extinction (A(V)) and of the ratio of total to selective extinction (R), derived from the 1989 Cardelli, Clayton, & Mathis fitting of the interstellar extinction law, is presented and applied to a set of 1900 color excesses derived from observations of stars in UBVRIJHKL. The method is used to study the stability of A(V) and R within selected regions in Perseus, Scorpius, Monoceros, Orion, Sagittarius, Ophiuchus, Carina, and Serpens. Analysis shows that R is approximately constant and peculiar to each sector, with mean values that vary from 3.2 in Perseus to 5.6 in Ophiuchus. These results are similar to published values by Aiello et al., He et al., Vrba & Rydgren, O'Donnell, and Cardelli, Clayton, Mathis.